Secondary immunodeficiencies are common in cancer, aging, autoimmunity, AIDS, and other viral and bacterial diseases. It has long been thought that treatment of these secondary immunodeficiencies would result in improved prognosis in these diseases. Despite much experimental effort, so far only levamisole and isoprinosine have been extensively licensed and employed clinically for such treatments. There is a need for more effective drugs of this type.
Immune function includes the humoral and cellular arms of the immune system as well as those aspects dependent on macrophages and granulocytes. The various aspects of immune function can be augmented or modified by various agents which can, in general, be referred to as immunopotentiators. Immunopotentiators, including drugs and biological substances, have been extensively employed in the prevention and treatment of human diseases.
However, recent work (Sad and Mosmann, 1994; Sieling et al., 1994; Chakkalath and Titus, 1994; Tripp et al., 1994; Bogdan et al., 1991; Fiorentino et al., 1989) suggests that improper stimulation of the immune response may actually facilitate the disease process. It appears in both murine and human models that the cytokine profile of immune response is regulated by which one of the subclasses of T helper (Th) cells, Th1 or Th2, is activated in response to the pathogens. Tht cells, in general, have a pattern of secreting IL-2, IFN-.gamma. and lymphotoxin, while the Th2 general secretion pattern is IL-4, IL-5, IL-6, IL-9, IL-10 and IL-13. The Th1 cell cytokine profiles are generally associated with disease resistance and Th2 cytokine profiles with progressive disease. In particular, it has been shown that for intracellular pathogens, such as Mycobacterium leprae, Listeria monocytogenes and Leishmania major, the cytokine profile from Th1 cells is necessary to restrict the growth of the pathogens. Many factors determine which subset of T-cells is activated during the immune response and it appears that it is a combination of factors, including IL-12 from activated macrophages, that lead to a Th1 response. In these diseases, it would be useful to have a means of augmenting or stimulating the Th1 response. For example in leprosy, patients do not express the type 1 response, rather their lesions express the type 2 cytokines which are typical of humoral responses and immunosuppression of the cell mediated immunity needed for resistance to intracellular pathogens.
One class of immunopotentiators has been derived from purine structures such as inosine or hypoxanthine, e.g., isoprinosine (a synthetic drug complex composed of inosine and the p-acetamido-benzoate salt of N,N-dimethylamino-2-propanol in a molar ratio of 1:3; DIP salt). ##STR2## and NPT 15392 (9-erythro-2-hydroxy-3-nonyl-hypoxanthine) ##STR3## These compounds have been classified as "thymomimetic drugs" (Hadden, 1985) in that they stimulate the immune system by actions primarily on thymus-derived (T) lymphocytes, although they do act on other cells involved in immune responses. Isoprinosine is one example of a medically useful thymomimetic drug which is licensed for human use in a number of countries around the world. The action of isoprinosine in vitro is paralleled by inosine and potentiated by the complex with DIP salt (Hadden, 1978). The action of isoprinosine in vivo is not achieved with inosine or DIP salt alone (Wybran et al., 1982), suggesting to applicants that complex formation and protection of the inosine base is critical for in vivo activity.
The search for more immunologically active molecules of this type for clinical use has generated a considerable literature. U.S. Pat. No. 3,728,450 to Gordon discloses complexes formed by inosine and amino-alcohols which have pharmacological activity in combatting influenza or herpes virus.
U.S. Pat. No. 4,221,794 to Hadden et al. discloses complexes of purine derivatives (9-(hydroxyalkyl) purines) with amino-alcohol salts of p-acetamidobenzoic acid which have immunomodulating and antiviral activity.
U.S. Pat. No. 4,221,909 to Hadden et al. discloses p-acetamidobenzoic acid salts of 9-(Hydroxyalkyl) purines useful as viricides, immunoregulators and anti-leukemia agents.
U.S. Pat. No. 4,340,726 to Giner-Sorolla et al. discloses esters (purine compounds) having immunomodulator, antiviral, antitumor and enzyme inhibitor activity.
U.S. Pat. No. 4,221,910 to Giner-Sorolla et al. discloses 9-(hydroxyalkyl) purines useful as immunopotentiators, viricides and antileukemic agents.
U.S. Pat. No. 4,457,919 to Giner-Sorolla et al. discloses purine derivatives which have immunomodulating, antiviral and antitumor activity.
U.S. Pat. Nos. 4,510,144 and 4,387,226, to Giner-Sorolla et al., disclose dihydrothiazolo purine derivatives with immunomodulating activity.
Japanese Laid-Open Patent Application Number 58-140100 discloses (heptamin-1-ol)-5'-adenosine-monophosphate. Saha et al. (1988) discloses its activity in potentiating the in vitro primary humoral immune response against a T cell-dependent antigen (sheep red blood cells) when present in the early phase of spleen cell culture. Saha et al. (1987) discloses the activity of HAA in augmenting anti-SRBC PFC activity and antibody titer values in ICR male mice. They also show the activity of HAA in increasing anti-SRBC PFC activity and antibody titer values in spontaneously hypertensive rats.
Hadden et al. [1983] indicates that purines, particularly inosine-containing or inosine-like compounds, where examined, generally share the capacity to mimic thymic hormone action to induce precursor T-cell differentiation and to potentiate functional responses of mature T-cells, particularly the Th1 cells in response to infections of intracellular pathogens. One example of these molecules, transfer factor, was hypothesized to contain inosine-5'-monophosphate (IMP) in its more elaborate structure (Wilson and Fudenberg, 1984).
It would be useful to have available these immunomodulating/immunopotentiating compounds for use as discussed herein below.
Viral infections and intracellular bacterial pathogens are a major public health concern. In both these categories, the bacterial and viral pathogens avoid the host immune system because they grow within the host's cells. A cell-mediated immune (CMI) response by Th1 cells initiated by macrophages is the general mode of host defense or resistance against intracellular pathogens once infection has occurred. An effective antibody response in response to vaccination can confer immunity.
While treatment for the bacterial diseases via antibiotics is available, the increasing drug resistance of bacteria makes it necessary to look at other avenues for treatment. One way of treating infected individuals is to increase the effectiveness of their immune system. In these diseases, the presence of sensitized T lymphocytes and activated macrophages is the key factor in immunity. Therefore, effective treatments for these diseases must activate macrophages and sensitize the appropriate T lymphocytes (Ryan in Stites and Terr, pages 637-645 and Mills in Stites and Terr, pages 646-656).
Intracellular bacterial pathogens include Salmonella, Legionella, Listeria, Mycobacteria and Brucella. Salmonella species are members of the Enterobacteriaceae and cause a significant portion of enteric disease, including typhoid fever. The capsule of S. typhi has a surface capsular antigen and antibody against the capsular antigen is not protective. In fact, many carriers of typhoid have high levels of antibodies against the pathogen.
Studies of Legionella show that it is an obligate intracellular parasite of macrophages. Lisreria is gram-positive causing meningeal infections and sepsis in adults and a variety of infections in neonates. The primary role of defense against these pathogens has been shown to be T-lymphocyte associated macrophage activation. Studies of Bruceila associated disease have also shown that antibody does not confer protection and that activated macrophages produced by specifically sensitized T-lymphocytes do protect.
It would be useful to have effective drugs for these diseases that activate macrophages and sensitize the appropriate T lymphocytes to the pathogen.
In general, there are few or no effective anti-viral drugs and, therefore, protection from viral pathogens also remains a major public health goal. Vaccination remains the best source of protection in viral diseases. However, often vaccines do not confer immunity because of: (1) a poorly immunogenic viral antigen; (2) the lack of time between vaccination and exposure; or (3) the inability of the vaccinated individual to respond.
For example, influenza vaccines must constantly be updated as the virus undergoes antigenic variation. Often the most current vaccine is not available, or not in full production, prior to the start of the winter months, which are the peak epidemic months. Therefore, those receiving the vaccine may be exposed to the virus in the environment before antibody titers are available. Further, among patients at higher risk, i.e. elderly and young, there is often a reduced compliance until an epidemic starts. In addition, influenza strikes particularly hard in the young and elderly populations and also individuals with underlying cardiorespiratory disease. These particular groups often have a less vigorous immune response to the vaccine.
Influenza viral infection suppresses normal pulmonary antibacterial defenses so that patients recovering from influenza have a greatly increased risk of developing bacterial pneumonia. It appears that there is an impairment of alveolar macrophages or neutrophils during influenza viral infection.
Therefore, a means of enhancing the immune response to influenza viral infection or of enhancing resistance to bacterial pneumonia would be useful in treating this disease. One possible way of increasing the efficacy of treatment is by treating with substances possessing immunopotentiating properties (Hadden et al., 1976; Hadden, 1987).
Chronic hepatitis B infection is a major public health concern. The hepatitis B virus is the cause of acute and chronic hepatitis, as well as hepatic carcinoma. The acute disease is self-limiting while the chronic infection persists for the life of the host. Chronic carriers remain infectious for life. It is estimated that there are over 100 million carriers world wide.
There are no currently effective treatments for the disease. Prevention, via vaccination, remains the only solution. Vaccination for those at risk is critical (James et al., 1991; Mills, 1991). However, upon vaccination with hepatitis B virus surface antigen (HBsAg), nearly 2% to 15% of those vaccinated have been found not to produce antibodies to the hepatitis B virus surface antigen (anti-HBs) and are thus not protected against this infection, in other words, they are nonresponders (Deinhardt, 1983). Various schemes of multiple administrations of the antigen preparation are recommended to induce intense immunity against hepatitis B (Grossman and Cohen, 1991). However, there is still a pool of nonresponders. Therefore, an alternative means of enhancing the immunogenicity of vaccine preparations against hepatitis B is needed to solve this important public health need.
People at high risk of infection are most frequently found among patients undergoing chronic hemodialysis treatment (Ferguson, 1990; Walz et al., 1989), those with HIV-infection and other immunocompromised patients (Hess et al., 1989). Those who come into contact with these groups and have not previously had contact with hepatitis B virus, face the highest risk of infection and, therefore, need rapid and maximal protection from the infection. This is particularly acute among health-care providers (Grossman and Cohen, 1991). Therefore, nonresponders to the currently available vaccine against hepatitis B in these groups are at even greater risk of infection.
It would be useful to be able to increase the efficacy of vaccination within the nonresponder groups. One possible way of increasing the efficacy of prophylaxis is the enhancement of the immunogenicity of available vaccines by using biologically active substances possessing adjuvant properties (Byars and Allison, 1989).
It is well known that adjuvants are able to stimulate antibody formation in response to heterologous antigens. Adjuvants are defined as compounds capable of potentiating an immune response and are, therefore, one class of immunopotentiators (Stites and Terr, 1991). Adjuvants are used to increase the immune response in vaccination (Seaman, 1991). For example, in vaccine preparations with hepatitis B, HBsAg is generally absorbed onto aluminum hydroxide to enhance the immunogenic effect in order to achieve a protective titer of anti-HBs (&gt;10 IU/1) which prevents infections.
However, as stated above, there is a group of nonresponders who do not respond even to this augmented vaccine (Celis et al., 1987; Meuer et al., 1989). This lack of protective immunity by vaccination appears due, in part, to components of the immune response determined at the level of the major histocompatibility complex (MHC) (Alper et al., 1989; Walker et al., 1981). It has been suggested that "non-responders" lack a dominant gene of the immune response in the MHC and, as a result, synthesis of anti-HBs occurs, at most, at low levels that can barely be detected by currently applied methods of detection (Thomson et al., 1977). Similarly, immune response genes associated with the murine major histocompatibility complex (H-2) have been shown to control cellular and humoral responses to determinants on numerous T-cell-dependent antigens, including HBsAg.
The results obtained in combined application of hepatitis B vaccine and various immunomodulators point to the expediency of this approach, since combination treatment can reduce the number of persons who either do not completely respond or respond with low levels of anti-HBs (Celis et al., 1987; Meuer et al., 1989). However, while the data are encouraging, there still exist persons who do not respond to these treatments and for whom it would be useful to have an adjuvant boosted hepatitis B vaccine which promotes rapid induction of maximal levels of specific antibodies and increase protection in the nonresponder population.
Hadden et al. (1983) indicates that purines, particularly inosine-containing or inosine-like compounds, where examined, generally share the capacity to mimic thymic hormone action to induce precursor T-cell differentiation and to potentiate functional responses of mature T-cells.
Isoprinosine has shown some efficacy in the treatment of lethal influenza challenge in mice; and, when administered with a subinfectious dose of virus, it prevented mortality on subsequent challenge with virus (Glasky, 1985). Isoprinosine is licensed in several countries for human use in influenza therapy based upon its clinical activity in man (Glasky, 1985). However, the half-life of isoprinosine in man is less than four hours; and, therefore, it is not very effective for in vivo treatments. Isoprinosine is rapidly hydrolyzed, thereby causing the short half-life in vivo. Inosine in vitro (Hadden, 1978) has similar properties to isoprinosine, but in vivo it is rapidly catabolized so that its half-life is even shorter than isoprinosine and thus it has no activity in vivo (Wybran et al., 1982). It would be useful to have more stable inosine-like compounds with greater immunopotentiating capabilities.